To a large extent, functional groups or moieties in a polymer determine the physical characteristics of that polymer.
The presence of functional groups such as urethanes or amides in polymers results in formed polymers having improved properties such as toughness, cross-linking feasibility, hydrogen bonding and so forth. Theoretically, amide and urethane functionalities can be incorporated into polyesters and polyurethanes as amide diols and urethane diols. The amide and urethane moiety would thus be attached to the polymer backbone.
Diamide diols and urethane diols are known. Diamide diol synthesis is difficult and generally results in low purity materials. Further, these diamide diols are solid and incompatible with most systems such as with diisocyanate for urethane type polymers. For this reason, these have not become a polyol of choice in common systems such as polyurethanes. Further, although the synthesis of diamide diols by reacting a dicarboxylic acid with ethanolamine is known it is not straight forward and provides a low purity product.
Synthesis of diamide diols involves the reaction of two to three fold excesses of ethanolamine at around 150.degree. C. followed by removal of excess ethanolamine together with water. From a commercial point of view, this synthesis is not practical since it requires the use of excess ethanolamine. The problem of using equal or slightly more than equivalent amounts of ethanolamine is that the reaction at later stages is very slow. Using higher reaction temperature usually results in some dehydration of diamide diols giving oxazolidone as a by-product.
Formation of urethane diols by reacting ethanolamine with ethylene or propylene carbonate generally must be carried out at temperatures near 60.degree. C. in order to prevent cyclization yielding oxazolidone. But this by itself does not present significant problems.
Several references which discuss amide diols, urethane diols and polymers incorporating either of these include Rose, U.S. Pat. No. 3,025,323; Levy, U.S. Pat. No. 3,458,456; Katayama, U.S. Pat. No. 3,786,031; Martorano, U.S. Pat. No. 4,190,693,; Lin et al, U.S. Pat. No. 4,448,905 and Moller, U.S. Pat. No. 4,143,159.
The Katayama patent discloses the reaction to form a polyamide urethane or polydiamide urethane. This is an extremely complex reaction which incorporates the basic starting unit N-6-hydroxycaproyl amino alcohols or N,N'-di-(6-hydroxycaproyl)-diamines and diisocyanates.